1. Field of the Invention
The invention relates to a heat treatment process for material bodies made of nickel base superalloys.
2. Discussion of Background
Heat treatment processes of this kind for material bodies made of nickel base superalloys are known from U.S. Pat. No. 4,643,782, which describes nickel base superalloys with the trade name "CMSX", from which monocrystal components can be cast, in particular blades for gas turbines. Such a nickel base superalloy having the designation "CMSX-4" is essentially composed of (in % by weight): 9.3-10.0 Co, 6.4-6.8 Cr, 0.5-0.7 Mo, 6.2-6.6 W, 6.3-6.7 Ta, 5.45-5.75 Al, 0.8-1.2 Ti, 0.07-0.12 Hf, 2.8-3.2 Re, remainder nickel.
According to U.S. Pat. No. 4,643,782, these nickel base superalloys are subjected to a heat treatment in order to dissolve the .gamma.' phase and the .gamma./.gamma.' eutectic and to produce regular .gamma.' particles in an aging process.
However, due to excessively high stresses in the casting process between mold and casting, uncontrollable recrystallizations may occur following solution annealing of the castings, which leads to high reject rates during production. Furthermore, due to the low cooling rates in the monocrystal casting process, a coarse .gamma.' structure is formed in the casting compared to conventional castings. In addition, the dendritic segregation in the monocrystal casting process is higher, which leads to a lower phase stability. Good diffusion annealing is therefore required in order that no brittle phases should be deposited during use, i.e. aging, of the monocrystalline casting.